Many nurseries have thousands of potted plants in their inventory. In order to maintain a correct level of nutrients for the plants nurseries will apply time release dry fertilizers to the soil surface. In the past methods for such application included manual application using a cup or spoon, broadcasting which wastes expensive fertilizer, or use of a variety of mechanical applicators which are complex and may damage the fertilizer time release coating by physical value closure.
Large well established nurseries may be able to afford the more expensive mechanical applicators, however many smaller or more specialized growing operations may be unable to afford the expensive mechanical applicators and their maintenance costs.
Existing applicators are prone to jamming, clogging, or are difficult to use productively. Or conversely, they have multiple parts, require a blower or other power source and thus are expensive to manufacture. A large number of existing patents disclose a variety of dispensing methods. Each method requires manually or electronically operated valve or else does not control the amount of material dispensed.
A first example is U.S. Pat. No. 6,981,457 B2 which consists of an implement mounted cylinder with baffles at the lower end. As the implement (such as a rake) is moved, material moves through the baffles and is dispensed to the ground. While simple, this device has no method for exactly controlling the amount of material applied.
The next example is U.S. Pat. No. 2,772,815 which teaches a rotating paddle wheel for metering controlled amounts of material for application. This method is subject to clogging and jamming and also may damage fragile coatings on time-release fertilizers.
U.S. Pat. No. 5,339,994 shows a dual valve system for metering fixed amounts for application. Again this approach may harm coatings and is subject to jamming from material build-up.
U.S. Pat. No. 7,641,082 B2 has an electronically operated valve for dispensing a controlled amount of material. The use of a microprocessor and other electronics for control makes the manufacture of this device relatively expensive. Also a mechanically operated valve can still damage coatings.
Other patents reviewed include U.S. Pat. No. 4,387,852, U.S. Pat. No. 5,101,744, U.S. Pat. No. 5,431,115, and U.S. Pat. No. 4,934,288.
As seen above, there are a variety of dry material applicators that have been disclosed. Each device may be prone to clogging or jamming, may not accurately meter the correct amount of material, may damage material by mechanically closing a valve, or may be costly to manufacture. An ideal dispensing apparatus would be simple with few moving parts, gentle on the dispensed material, resist clogging and jamming, and be easy to use for long periods.